1. Field of the Invention
The present invention generally relates to an active device array substrate and a fabrication method thereof, and more particularly, to an active device array substrate and a fabrication method thereof which uses a multi-tone mask for reducing the number of masks required for fabricating the active device array substrate.
2. Description of Related Art
Presently, multimedia technology has become very developed due to the advancement of semiconductor devices or display apparatuses. Among various displays, thin film transistor liquid crystal display (TFT-LCD) has become the mainstream in today's display market for it has such characteristics as high image quality, high space efficiency, low power consumption, and no radiation.
A TFT-LCD includes a TFT array substrate, a color filter substrate, and a liquid crystal layer between the TFT array substrate and the color filter substrate. Generally speaking, at least five mask processes are required to fabricate a conventional TFT array substrate. The first mask process is used to define a gate and a scan line, the second mask process is used to define a channel layer, the third mask process is used to define a source, a drain, and a data line, the fourth mask process is used to define a passivation layer, and the fifth mask process is used to define a pixel electrode.
Because the number of mask processes performed will directly affect the fabrication cost and the fabrication time of the entire TFT array substrate, every manufacturer in the industry is trying to reduce the number of mask processes required for fabricating TFT array substrates. Therefore, a fabrication method of a TFT array substrate which can increase the throughput and reduce the fabrication cost is highly desired.